Interworking between radio access networks

ABSTRACT

The present invention discloses a method of interworking between different radio access networks. A radio transceiver device is capable of operating with the first radio access network and the second radio access network is attached to the first radio access network. The method comprises the steps of detecting a service request is requested. Information is accessed on conditions for the first and the second radio access network for giving sufficient support for a service requested by the service request. It is analyzed whether or not the first radio access network and the second radio access network meets the conditions, and a handover of the radio transceiver device from the first radio access network to the second radio access network is initiated if the second radio access network meets the conditions but the first radio access network does not. Thus, the present invention serves to support dual mode mobile stations and networks in such a way that the correct radio access which sufficiently supports a requested service is automatically obtained.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.09/911,219, filed on Jul. 23, 2001, which is a continuation ofinternational application number PCT/EP99/00452, filed on Jan. 25, 1999.The disclosures of the prior applications are hereby incorporated byreference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a method of interworking betweendifferent radio access networks which support different services orwhich support services with different qualities.

BACKGROUND OF THE INVENTION

The evolutionary development of the so-called 2^(nd) generation mobilenetworks towards the so-called 3^(rd) generation networks leads tonetwork configurations where both, 2^(nd) and 3^(rd) generation radioaccess networks, operate with the same core network CN. In the firstphase such 3^(rd) generation radio access networks RAN will cover onlyhot spots, i.e. regions with high radio traffic load, later they willcover wider and wider areas.

Thus, radio transceiver devices will have to be introduced which will beable to operate with either of the radio access networks. This kind ofradio transceivers is referred to as dual mode mobile stations MS.

In the GSM network two different accesses exist, i.e. GSM 900 and GSM1800. However, the GSM 900 and 1800 dual access differs from thesituation described above in that the GSM 900/1800 dual access offersthe same services to the subscribers through both accesses, whereas inthe 2^(nd)/3^(rd) generation dual access the difference between the tworadio access methods and the development of the core packet network leadto a situation where the same services are not necessarily specified,not to mention implemented in both the 2^(nd) and 3^(rd) generationaccesses. Even if the same services are specified, it may not beprofitable nor reasonable to implement them in all networks.

There are several services that most probably will be supported by onlyone of the radio access network types. Such services are, for example,non-transparent circuit-switched services which are redundant in the3^(rd) generation radio access network, but which are widely used in the2^(nd) generation radio access network (GSM network).

Furthermore, transparent circuit-switched services are redundant in the3^(rd) generation radio access network, since the 3^(rd) generationaccess network will be able to support a real-time packet transmission.On the other hand, transparent circuit switched services provide theonly real-time service in GSM.

Moreover, real-time packet services are not available in GSM, whereasthese services are available and important in the 3^(rd) generationradio access network.

Thus, these circuit-switched services are very important in the currentGSM networks. They will also be important in the foreseeable futurebecause of their wide acceptance and introduction in the networks andbecause the forthcoming GSM packet service (GPRS) cannot supportreal-time transmission.

In contrast thereto, the 3^(rd) generation network (UMTS, (universalmobile telephone system) will be able to support real-time packettransmission. This will make circuit-switched services redundant.Especially the implementation of the non-transparent circuit-switchedservices in the 3^(rd) generation access will be questionable due totheir redundancy, complexity and costs involved.

Thus, the dual mode mobile stations will have to operate in networkswith various degrees of service support. Some 3^(rd) generation accesseswill support only packet services, some both packet services andtransparent circuit switched services, some may even support both packetservices and non-transparent circuit-switched services (if everspecified for 3^(rd) generation radio access network). Some 2^(nd)generation accesses will support only circuit-switched services, someboth circuit-switched and (non-real-time) packet services.

Therefore, a new situation for the mobile stations arises. On the onehand, it is possible that a mobile station is attached to a 3^(rd)generation cell and is requested (or requests itself) a servicesupported only by the 2^(nd) generation access. Vice versa, it is alsopossible that a mobile station is attached to a 2^(nd) generation celland is requested (or requests itself) a service supported only by the3^(rd) generation access.

This leads to the drawback that in these situations only those servicescan be requested and used which are common to both a 2^(nd) generationradio access network and a 3^(rd) generation radio access network.

In addition, in case of services supported by both networks, there areseveral services which are supported with different qualities bydifferent radio access networks. For example, the different radio accessnetworks can provide different communication bit rates. Moreover, theprice of connection can be different. For example, UMTS will be mostprobably more expensive in beginning, whereas later on GSM could be moreexpensive. Furthermore, the same services can be provided with differentdelays. In the prior art, these differences are not taken into account.

Thus, the above described drawbacks of the prior art result in a limitedusability of a respective mobile station.

SUMMARY OF THE INVENTION

Hence, the object underlying the present invention resides in providinga method by which the above described drawbacks are removed.

This object is achieved by a method of interworking between differentradio access networks. In detail, in this method, a radio transceiverdevice capable of operating with the first radio access network and thesecond radio access network is attached to the first radio accessnetwork. The method comprises the steps of detecting a service request,accessing information on conditions for the first and the second radioaccess network for giving sufficient support for a service requested bythe service request, analysing whether or not the first radio accessnetwork and the second radio access network meets the conditions, andinitiating a handover of the radio transceiver device from the firstradio access network to the second radio access network if the secondradio access network meets the conditions but the first radio accessnetwork does not.

As an alternative, according to the invention the above object is solvedby a network interworking device for a telecommunication networkcomprising at least two radio access networks. For this device, a radiotransceiver device capable of operating with the first radio accessnetwork and the second radio access network is attached to the firstradio access network. The device comprises a detecting means fordetecting a service request. Furthermore an analysing means responsiveto the detecting means is provided which comprises the functionality ofaccessing information on conditions for the first and the second radioaccess networks for giving sufficient support for the a servicerequested by the service request and analysing whether or not the firstradio access network and the second radio access network meet theconditions. Moreover, the network interworking device comprisesinitiating means responsive to the analysing means, the initiating meansbeing adapted to initiate a handover of the radio transceiver devicefrom the first radio access network to the second radio access networkif the respective conditions are not met by the first radio accessnetwork but by the second radio access network.

Further advantageous developments are defined in the dependent claims.

By the above-mentioned method, the drawbacks of the prior art areremoved. That is, by the method according to the invention, a situationcan be handled in which a service is provided which is not supported bya currently used radio access network but by another one. This isachieved by effecting a handover from the first to the second radioaccess network.

In addition, it is also possible to initiate a handover in case aservice is more sufficiently supported by the second radio accessnetwork than by the first one. Thus, the present invention provides amore flexible usability of the mobile stations.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more readily understood with reference tothe accompanying drawings in which:

FIG. 1 shows a general network architecture in a schematic blockdiagram;

FIG. 2 shows a flowchart of a process performed by the networkcontrolling device according to the first embodiment of the presentinvention;

FIG. 3 shows a flowchart of a process performed in an analysing step S12of FIG. 2,

FIG. 4 shows a flowchart of a process performed by a radio transceiverdevice according to the second embodiment of the present invention, and

FIG. 5 shows a device in which the method according to the invention iscarried out.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

According to the invention, a service request is analysed and comparedwith the capabilities of a first radio access network RAN-A on which amobile station is currently located.

If the radio access network RAN-A does not support the requested serviceor does not support the requested service sufficiently, but the corenetwork does support the service, a handover is initiated to the otherradio access network RAN-B which supports the requested servicesufficiently and has coverage in the area.

Thus, the method according to the present invention serves to supportdual mode mobile stations and networks in such a way that the correctradio access which supports the requested service sufficiently isautomatically obtained.

This method can be performed in a network control device (for example, amobile services switching center, MSC, or an interworking unit, IWU, ora base station controller, BSC, or a packet network node, PNN) or in theradio transceiver device (mobile station). The method can be performedby the network control device in case the service requested isspecified, for example, in international standards, but not implementedin the network. In contrast thereto, if it is not specified, the methodcan be carried out either in the radio transceiver device or in thenetwork control device.

Hereinafter, the general network architecture is described withreference to FIG. 1.

A core network CN comprises at least one packet network node PNN and oneMSC (mobile services switching center) and one IWU (interworking unit).For simplifying the diagram, the interconnections between the PNN, theMSC and the IWU are not shown. The core network CN (i.e., the PNN, theMSC and/or the IWU) communicates with a radio access network RAN-A and aradio access network RAN-B. Each radio access network has at least onebase station controller BSC_A and BSC_B.

In this example, only one cell Cell_A_1 of the network RAN-A and onecell Cell_B_1 of the network RAN-B are shown in FIG. 1. The cellCell_A_1 is provided with a base station BS_A_1, and the cell Cell_B_1is provided with a base station BS_B_1. The base stations BS_A_1 andBS_B_1 communicate with the base station controllers BSC_A and BSC_B.

The cells Cell_A_1 and Cell_B_1 have an overlapped region in which theradio access network RAN-A and the radio access network RAN-B can beaccessed.

For the purpose of following description, it is assumed that a mobilestation MS is located in this overlapped region. The mobile station MSis capable of communicating with both radio access networks. That is,the mobile station MS is adapted to both radio access networks and ispresent in the same coverage area. For example, the mobile station MSmay be a dual mode phone.

Depending on the reason why a service is not supported by the firstradio access network RAN-A sufficiently, there are various scenarios asto how, and by which means, the method of the present invention can copewith these situations.

In principle, the method can either be carried out in the mobile stationMS or in the network controlling device MSC or IWU or BSC or PNN.Hereinafter, these two cases are described in two embodiments. Moreover,in both cases it can further be distinguished between amobile-originated and a mobile-terminated case.

First Embodiment

The first case is described as a first embodiment of the invention. Inthis embodiment, a method is described which is performed in a networkcontrol device (e.g., MSC, IWU, BSC or PNN) of the core network CN.

It is assumed that a mobile station MS is located in the first radioaccess network RAN-A. The mobile station MS requests a service which isspecified (for example, in international standards) but which is notimplemented in the first radio access network. Since the service isspecified in general, the mobile station can assume that the service isalso specified in the current first radio access network RAN-A. However,the mobile station MS cannot know whether this service is implemented inthe network or not, that is, whether the requested service is supportedby the first radio access network RAN-A or not.

On the other hand, the network is aware of its capabilities. Hence, thenetwork control device (e.g. MSC or IWU or BSC or PNN) can determinewhether the network supports the requested service or not. In case thenetwork does not support the requested service, the network can initiatea handover to another radio access network which supports this serviceand which has coverage in the area where the mobile station is located.

The same process can be carried out in case a requested service issupported by both radio access networks, but the requested service issupported more sufficiently by the second radio access network.

Thus, the requested service is analysed whether it is supported or notand whether there is a more sufficient support of this service byanother radio access network. That is, the analysis is carried byanalysing whether the radio access networks RAN-A and RAN-B meet certainconditions with respect to the requested service.

The simplest condition is whether the requested service exists in theradio access network in question, i.e., in the radio access networkRAN-A or not. Other conditions could be, for example, a condition forthe bit rate, delay requirements or the price of the connection.

In the following, an example is described in which a requested serviceis not supported by the first radio access network RAN-A.

This process is described with reference to a flowchart shown in FIG. 2.

In a first step S11, the process waits for a service request. When aservice request is received, the process proceeds to a second step S12,in which the service request is analysed and compared with thecapabilities of the radio access network RAN-A currently used by themobile station MS. For example, the analysis could be effected bycomparing the received service request with a set of services availablein the radio access network RAN-A. The list of available services can bestored in a table or the like. If it is determined that the servicerequest is supported sufficiently by the radio access network RAN-A, theprocess branches to a step S13 in which the normal processing of theservice request within the network is performed.

On the other hand, if it is decided in step S12 that the requestedservice is not supported sufficiently (as described above) by the radioaccess network RAN-A but by a second radio access network RAN-B, theprocess branches to a step S14. In this step S14, a handover to thesecond radio access network RAN-B is initiated.

In the following, a more concrete example of the present embodiment isdescribed, in which a service is implemented in only one of the tworadio access networks. The core network can be a GSM core networkcomprising a GSM radio access network and a UMTS (universal mobiletelephone system) radio access network. Non-transparent circuit-switchedservices are only implemented in the GSM network. In contrast thereto,the UMTS network supports packet services and, possibly, transparentcircuit-switched services, but no non-transparent circuit-switchedservices.

Now it is assumed that a dual mode phone is located in a UMTS cell andrequests a non-transparent circuit-switched data call. This couldhappen, for example, if a user wishes to communicate with a mail serverof a company or with a remote access server. The non-transparentcircuit-switched service is not supported by the UMTS network. However,it is specified there.

In this case, the above procedure is carried out. That is, the servicerequest is analysed. The network controlling device, i.e. the IWU(interworking unit) or the MSC (mobile services switching center) of theradio access network, detects that the requested service, i.e. thenon-transparent circuit-switched data call, cannot be performed in theUMTS network but is supported by the GSM network. Hence, a handover tothe cell of the GSM network is initiated, which has coverage in the areaof the cell of the UMTS network in which the mobile station MS islocated.

Thus, according to the first embodiment, it is possible to execute aservice which is requested by a mobile station and which is notsupported by the currently used radio access network (RAN-A) byperforming a handover to a second radio access network (RAN-B).Furthermore, it is possible to execute a requested service by that radioaccess network which supports the service more sufficiently. Thenecessary analysis of the service request is effected in the networkcontrol device (e.g. MSC or IWU or BSC) of the currently used radioaccess network (RAN-A), since the service is specified in general, butit is not clear to the mobile station MS whether this service isimplemented in the currently used radio access network (RAN-A).

In the following, an example is described in which a requested serviceis supported by both radio access networks RAN-A and RAN-B.

In this case the process performed is the same as described with respectto FIG. 2. However, since in this case the condition is not only whetherthe requested service is present or not, the analysis step S12 shown inFIG. 2 is described in more detail with respect to FIG. 3.

For determining whether the first or the second radio access networksupports the requested service more sufficiently, the conditions forthis have to be specified. That is, it is analysed whether the secondradio access network supports a service by a given amount better. Thisgiven amount can be defined by a norm or a threshold. In this example,the given amount can be, for example, 10% of the current bit rate of thefirst radio access network RAN-A. That is, in this case the conditionfor the second radio access network RAN-B supporting the requestedservice more sufficiently than the first radio access network RAN-A isthe condition that the bit rate is at least 10% higher.

The conditions as to whether the first radio access network RAN-Asupports the requested service more sufficiently than the second radioaccess network RAN-B can be set previously and stored in a database, forexample.

In the process shown in FIG. 3, the condition is obtained in step S121.Then, it is determined whether the condition is already met by thecurrently used first radio access network RAN-A. In the above example ofthe bit rate, the desired bit rate is compared with the bit rateprovided by the radio access network RAN-A, which can be supplied fromthe database, for example.

If it is determined in step S121 that the condition is met by the firstradio access network RAN-A, the flow branches to a step S125 in which“RAN-A” as the result of the analysis is output. That is, in the processshown in FIG. 2, the flow branches to step S13., in which a normalprocedure is carried out and the currently used radio access networkRAN-A is maintained. That is, in the above example of the bit rate,“RAN-A” is output if the desired bit rate of 10% higher than thecurrently used bit rate can already be provided by the current radioaccess network RAN-A.

On the other hand, if it is determined in step S122 that the conditionis not met by the first radio access network RAN-A, the process advancesto step S123 in which it is determined whether the condition is met bythe second radio access network RAN-B. If the condition is not met bythe second radio access network RAN-B, the flow branches to the stepS125. That is, the mobile station MS maintains the connection to thefirst radio access network RAN-A. In the above example of the bit rate,this occurs in case the bit rate is, for example, only higher by about5%.

However, in case that the condition is met by the second radio accessnetwork RAN-B, the flow branches to a step S124, in which “RAN-B” isoutput as the result of the analysis step. That is, in the process shownin FIG. 2, the process advances to the step S14 in which a handover tothe second radio access network RAN-B is initiated.

In the above example, the threshold by which the condition is analysedis set on such a value that a handover is not always initiated. That is,in the above example, it is taken into account that a handover is onlyinitiated in case bit rate provided by the second radio access networkRAN-B is considerably higher than the bit rate of the currently usedradio access network RAN-A. As a matter of course, this threshold can bevaried as necessary. That is, if it is desired, the threshold can be setsuch that the handover is initiated simply in case that the bit rate ofthe second radio access network RAN-B is higher.

Moreover, as a matter of course the condition for a handover from thefirst to the second radio access network is not limited on the bit ratebut can be plurality of different conditions as the price of connection,delay requirements, stability of the connection (for example, signalstrength etc.) and others.

Furthermore, a plurality of conditions can be combined or made dependenton each other. For example, a first condition for a service can be ahigher bit rate, and a second condition the price of connection. Acombined condition for initiating a handover to the second radio accessnetwork RAN-B can be that the second radio access network RAN-B has aconsiderably higher bit rate, but that the price of connection is onlymoderately higher than that of the currently used first radio accessnetwork RAN-A.

Modifications of the First Embodiment

In the preceding section, the first embodiment has been described for amobile-originated case. However, the process according to thisembodiment is also applicable to a mobile-terminated case. There, aservice request from outside the radio access network in which themobile station MS is located is to be analysed. Nonetheless, the abovesteps S12 to S14 remain the same.

Second Embodiment

Next, as a second embodiment, the above mentioned second case will bedescribed in which the mobile station itself performs the analysis of aservice request.

As in the above first embodiment, the mobile station MS is located in acell of the first radio access network RAN-A. In principle, the sameprocess performed in the network control device as according to thefirst embodiment can be carried out. However, in this case it is assumedthat the mobile station MS requests a service which is not specified(for example, in international standards) for the RAN-A type access.Thus, the mobile station MS knows that this service is not supported bythe radio access network in which it is located.

Consequently, in a mobile-originated case, the mobile station MS itselfanalyses the service request, which is issued by, for example,application software or the terminal (TE), i.e. the mobile stationitself, and compares it to the capabilities of the currently used radioaccess network RAN-A. If it is determined that the radio access networkRAN-A cannot support the requested service, but the second radio accessnetwork RAN-B can, the mobile station MS initiates or requests ahandover to the RAN-B type of access.

The above process is described with reference to a flowchart shown inFIG. 4.

As mentioned above, this process is performed in the mobile station MS.In a first step S21, the process detects whether a service request isrequired or not. The service request can be issued by an application inthe mobile station or by the terminal (TE), i.e. the mobile stationitself. When it is detected that a service request is desired, theprocess proceeds to a second step S22. In this step S22, the servicerequest is analysed and compared with the capabilities of the radioaccess network RAN-A currently used by the mobile station MS. Theanalysis can be similar to that in step S12 according to the firstembodiment. If it is determined that the service request is supported oris supported more sufficiently by the currently used radio accessnetwork RAN-A, the process branches to a step S23 in which theconnection with the radio access network RAN-A is maintained and theservice request is issued.

On the other hand, if it is decided in step S22 that the servicerequested is not supported by the radio access network RAN-A (that is,is not implemented in the radio access network RAN-A), but by the secondradio access network RAN-B, the process branches to a step S24. In thisstep 24, the mobile station MS itself initiates or requests a handoverto the second radio access network RAN-B.

As in the description of the first embodiment, in the following a moreconcrete example of the second embodiment is described. Likewise as inthe former example, the core network is a GSM core network comprising aGSM radio access network and a UMTS (universal mobile telephone system)radio access network. The UMTS supports packet service and, possibly,transparent circuit-switched services, whereas in the UMTS nonon-transparent circuit-switched services are specified, since theseservices are regarded as redundant due to the presence of packetservices.

In this situation, a dual mode phone is located in a UMTS cell. It isnow assumed that the application or the user of the mobile stationrequests a non-transparent circuit-switched call. This could happen, forexample, in case the user wishes to access a mail server of his companyor a remote access server.

Now, the mobile station MS analyses the service request. The mobilestation MS determines that the mobile station is currently located in aUMTS radio access network that does not support the non-transparentcircuit-switched service. However, the GSM radio access network supportsthe requested service. Hence, the mobile station initiates or requests ahandover to a cell of the GSM radio access network which has coverage inthe area of the cell of the UMTS network in which the mobile station MSis located.

Thus, according to the second embodiment, it is possible to execute aservice which is requested by a mobile station and which is notspecified by the current radio access network (RAN-A) by performing ahandover to a second radio access network (RAN-B). The necessaryanalysis of the service request is effected in the mobile station, sincethe service is not specified in the currently used radio access network(RAN-A), and hence it is clear that this service is not supported bythis network.

Moreover, according to the second embodiment, the process described withrespect to FIG. 2 can be carried out in the same way as according to thefirst embodiment. That is, the process performed in the analysis stepS22 can be the same as that shown in FIG. 2. Therefore, a description ofthis process as carried out in the mobile station MS is omitted here.

Modifications of the Second Embodiment

Regarding the second embodiment, modifications similar to thosedescribed in the first embodiment are possible. That is, although amobile-originated case has been described above, also amobile-terminated case is possible. In this case, a service request fromoutside the radio access network in which the mobile station MS islocated is to be analysed. The service request can be analysed in themobile station. However, it is preferable that the network (i.e., thenetwork controlling device MSC or IWU) analyses the service request andinitiates the handover, if necessary. In this case, a process similar tothe one according to the first embodiment is executed.

Furthermore, in case of both embodiments, it is possible that a serviceis requested which is neither supported by the first radio accessnetwork RAN-A nor by the second radio access network RAN-B. Moreover, itis also possible that a service is requested which is supported by noneof other available radio access networks. In this case, an errorprocedure can be initiated. This can be effected, for example, in amodified analysing step S12 or S22. The error procedure could, forexample, issue a corresponding notification to the mobile station andits user.

In both embodiments the service request is analysed as to whether therequested service is supported better by the currently used radio accessnetwork RAN-A or by the second radio access network RAN-B. This analysiscan be performed, for example, by comparing the requested service withall services available in the radio access network. Thus, especially inthe case of the second embodiment, the mobile station MS must have alist of all these services. This list can be provided by the networkcontrolling device during establishment of a call, for example. That is,information regarding the services supported by the respective radioaccess network could be incorporated in the BCCH signal. During a call,the above information could be incorporated in the DCCH signal.

The above examples of the embodiments describe a handover from a UMTS toa GSM radio access network. However, it is obvious that the handover canalso be effected in the other direction.

Hereinafter, an example for such a handover in the other direction isdescribed. It is assumed that a mobile station MS is located in a GSMradio access network. In this situation, a real-time packet service isrequested, either by the terminal application or by the core packetnetwork. The network (in the first embodiment) or the mobile station MS(as in the second embodiment) analyses the service request, determinesthat the mobile station MS is currently in a GSM radio access networkthat does not support the requested real-time packet service andinitiates a handover to a cell of a UMTS radio access network in thisarea.

In the following, examples of the above-mentioned analysis of theservice request according to the invention are described.

Concerning circuit switched services as the requested service, themobile station MS requests a service by sending a SETUP message to thenetwork. The SETUP message contains (among other things) a BearerCapability Information Element (BCIE). The BCIE carries detailedparameters related to the requested service, e.g. data rate, connectiontype (transparent/non transparent), mode (asynchronous/synchronous).

In a mobile terminated call the BCIE comes from ISDN or from the HomeLocation Register (HLR) of the GSM network.

The (GSM) network control device MSC analyses the BCIE parameters inorder to check whether the requested service is supported by the network(and whether the subscriber is entitled to use the service) and to huntand set up relevant sources in the MSC IWF (interworking function of thenetwork control device MSC).

Within this invention, the BCIE information is used by the networkcontrol device (e.g. MSC or BSC or IWU) or by the mobile station MS todecide whether a handover to another radio access network is required.

Concerning packet switched services as the requested service, the mobilestation MS requests a service by creating a PDP (Packet Data Protocol)context. This is effected by sending a data packet to the network. Thedata packet contains (among other things) a Quality of Service (QoS)request. The QoS defines for example whether the requested connectionshall be “real time” (i.e. whether a certain data rate is to beguaranteed and a certain delay is not to be exceeded).

In a mobile terminated packet connection the corresponding informationcomes from the core packet network CN.

The packet network node PNN analyses the QoS parameters in order to beable to deal accordingly with the packets belonging to this context.

Within this invention the QoS information is used by the network controldevice (e.g. packet data node or BSC or IWU) or by the mobile station MSto decide whether a handover to another radio access network isrequired.

In the following, an example of a device for carrying out the abovementioned method according to the first and second embodiments isdescribed with reference to FIG. 5. Reference numeral 1 denotes adetecting means which detects the service request, that is, whichperforms step S11 of FIG. 2 or step S21 of FIG. 4, i.e. the processshown in FIG. 3. The detected service request is supplied to ananalysing means 2, which performs the analysing step S12 of FIG. 2 orstep S22 of FIG. 4. In case the analysing means determines that ahandover is to be effected, the analysing means 2 supplies acorresponding handover request to an initiating means 3, which performsthe initiating step S14 of FIG. 2 or S24 of FIG. 4.

The analysing means 2 can be adapted such that it uses a database 4 fordetermining the conditions for a sufficient support of the requestedservice in the different networks. That is, in this database allservices of available radio access networks can be stored, includingtheir specifications like bit rate, price of connection, delays etc.

The above description and accompanying drawings only illustrate thepresent invention by way of example. Thus, the embodiments of theinvention may vary within the scope of the attached claims.

1. A method, comprising: detecting a service request, wherein saidservice request is received from a network side; accessing informationon conditions for a first and a second radio access network for givingsufficient support for a service requested by said service request,analysing whether or not said first radio access network and said secondradio access network meets said conditions; and initiating a handover ofa radio transceiver device from said first radio access network to saidsecond radio access network if the second radio access network meets theconditions but the first radio access network does not.
 2. A methodaccording to claim 1, wherein said conditions comprise a conditionwhether said requested service exists in the radio access network.
 3. Amethod according to claim 1, wherein said conditions depend on eachother.
 4. A method according to claim 3, wherein one of said conditionsfor the first radio access network is a given amount lower than thecorresponding condition for the second radio access network.
 5. A methodaccording to claim 1, wherein said method is performed in said radiotransceiver device.
 6. A method according to claim 1, wherein saidmethod is performed in a network control device.
 7. A method accordingto claim 6, further comprising the step of informing said radiotransceiver device of the fact that a handover to said second radioaccess network is to be initiated.
 8. A method according to claim 1,wherein said radio transceiver device is a dual mode phone which isadapted to be operated in said first radio access network and saidsecond radio access network.
 9. A method according to claim 1, whereineither said first or said second radio access network is a GSM network.10. A method according to claim 1, wherein either said second or saidfirst radio access network is a UMTS network.
 11. A method according toclaim 1, wherein said requested service is a circuit-switched service.12. A method according to claim 1, wherein said requested service is apacket service.
 13. A method according to claim 1, wherein an errorprocedure is initiated, when it is detected in said analysing step thatsaid requested service is not available in any of said networks.
 14. Amethod according to claim 13, in which said error procedure is anotification of the user.
 15. A method according to claim 1, whereinsaid radio transceiver device is attached to said first radio accessnetwork such that it is located in a cell of said first radio accessnetwork and connected by air with said first radio access network.
 16. Amethod according to claim 15, wherein said radio transceiver device isalso located in a cell of said second radio access network.
 17. A methodaccording to claim 1, wherein said analysing step also analyses whethera subscriber using said radio transceiver device is entitled to use saidrequested service.
 18. A network interworking device, comprising: adetecting unit configured to detect a service request, wherein saidservice request is received from a network side, an analyzing unitresponsive to said detecting unit and wherein the analyzing unit isconfigured to, access information on conditions for a first and a secondradio access networks for giving sufficient support for a servicerequested by said service request, and analyse whether or not said firstradio access network and said second radio access network meet theconditions, and initiating unit responsive to said analysing unit, theinitiating being configured to initiate a handover of said radiotransceiver device from said first radio access network to said secondradio access network if the respective conditions are not met by saidfirst radio access network but by said second radio access network. 19.A network interworking device according to claim 18, wherein saidinterworking device is configured in said radio transceiver device. 20.A network interworking device according to claim 18, wherein saidinterworking device is configured in a network control device.
 21. Anetwork interworking device according to claim 18, wherein saidanalysing unit is connected to a database to obtain informationregarding said conditions of said requested service.